Method for adjusting curvature of magnetic read/write head sliders

ABSTRACT

A method for adjusting the curvature of an air bearing surface (ABS) of a slider having a back surface opposite the ABS. The method includes steps of repeatedly measuring the curvature of the ABS and scribing lines (e.g. with a laser scribing tool) on the back surface to partially adjust the curvature of the ABS. In each measuring/scribing installment, the curvature of the ABS is measured and compared with a final target curvature to determine a curvature difference between the measured curvature and final target curvature. Each installment of scribing lines corrects for a predetermined percentage of the curvature difference. The predetermined percentage may be different in succeeding installments. Alternatively, each installment changes the curvature of the slider to match an intermediate target curvature. In a three-installment process, for example, there will be two intermediate target curvatures and a final target curvature.

FIELD OF THE INVENTION

This invention relates generally to laser scribing tools for scribingsemiconductor chips and the like. More particularly, it relates to amethod for scribing magnetic sliders so that they have an accuratecurvature on the air bearing surface (crown curvature and cambercurvature).

BACKGROUND OF THE INVENTION

Hard drives utilizing magnetic data storage disks are used extensivelyin the computer industry. Each magnetic data storage disk in a harddrive has an associated slider which is used to magnetically read andwrite on a disk surface. In operation, the magnetic data storage disksare rotated and a slider is held very close to the surface of each disksurface. The motion of the disk past the slider allows datacommunication between the slider and disk surface.

The distance between the slider and disk must be accurately controlled.Typically, the slider is shaped to fly upon a cushion of moving airformed by the rapidly moving disk surface. The surface of the sliderclosest to the disk surface is called an air bearing surface. The airbearing surface has a shape which is designed to provide a small butstable flying height between the slider and disk. The slider must nottouch the disk surface during operation because damage can result. Also,it is desirable to maintain as small a flying height as possible,because this increases the amount of data which can be stored. As flyingheight is reduced, it becomes increasingly difficult to maintain theflying height accuracy to the degree required for reliable recording andreading of data.

The shape of the slider has a substantial effect upon fly height. Morespecifically, the flying height is dependent upon the average curvatureof the air bearing surface of the slider. The curvature of the airbearing surface is often affected by the manufacturing processes used tomake the slider. Lapping of the slider (either the air bearing surfaceor a surface opposite to the air bearing surface) often causes stressvariations in the slider which distort the shape of the air bearingsurface. After lapping, it is almost always necessary (for high storagedensity applications) to adjust the curvature of the air bearing surfaceto a desired target curvature.

U.S. Pat. No. 5,266,769 to Deshpande et al. discloses a method ofadjusting the curvature of the air bearing surface of a slider byscribing a back surface of the slider. The scribing removes materialfrom the back surface, thereby releasing internal stress in the sliderand controllably changing the curvature of the air bearing surface.Scribing may be performed with a laser, sandblasting tool or the like. Acurvature measuring tool may monitor the curvature of the air bearingsurface as material is removed, thereby providing feedback control ifdesired. A problem with the method of Deshpande is that sliders are mostefficiently made in rows, and each slider in a row may have a differentamount of stress. This means that each slider must have a differentamount of material removed in order for the sliders to have the same airbearing surface curvature. Deshpande does not disclose a method forindividually controlling the curvature of sliders in a row. Deshpandeassumes that all sliders in a row require the same curvature adjustment.It would be an advance in the art to provide a row of sliders withindividually controlled curvature.

Further, Deshpande does not disclose specific, advantageous methods ofimplementing curvature control. The curvature of a slider may only bechanged ‘in one direction’ by removal of material from the back side ofthe slider and so the target curvature must not be overstepped.Deshpande does not disclose a method for curvature adjustment whichassures that the target curvature is not overstepped. Also, the changesin curvature caused by material removal from the back surface of theslider are not entirely predictable. When large changes in curvature arenecessary, the final curvature of the slider may be rather inaccurate.Deshpande does not disclose a method which provides the same accuracy incurvature control for large and small curvature adjustments. Therefore,there are many improvements which can be made to the method ofDeshpande.

OBJECTS AND ADVANTAGES OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea method of adjusting curvature of a slider that:

1) can be used to adjust the curvature of individual sliders stilljoined in a row;

2) assures that a target curvature is not overstepped;

3) provides the same accuracy in final curvature for a wide range in theamount of curvature adjustment required.

These and other objects and advantages will be apparent upon reading thefollowing description and accompanying drawings.

SUMMARY OF THE INVENTION

These objects and advantages are attained by a method for adjusting thecurvature of an air bearing surface (ABS) of a slider to match a finaltarget curvature. The slider has a back surface opposite the ABS. Themethod includes the steps of measuring the ABS curvature, determining acurvature difference between the measured curvature and final targetcurvature, and scribing lines to correct for a predetermined percentageof the curvature difference. The steps of measuring, determining, andscribing are repeated in at least two installments. The predeterminedpercentage may be different or the same in succeeding installments. Thefinal installment corrects for 100% of the remaining curvaturedifference.

Preferably, the scribe lines are spaced apart by a distance sufficientto ensure that the scribe lines act independently to affect thecurvature of the ABS. The scribe lines are spaced apart by a distance inthe range of about 5-200 microns, preferably in the range of about 20-80microns, and most preferably in the range of about 35-55 microns.

Preferably, the method includes the step of establishing a set of scribeline locations on the back surface where scribe lines can be located.The scribe line locations are spaced apart by a distance sufficient toensure that neighboring scribe lines act independently. Also preferably,in each installment, the average curvature change per scribe line issubstantially equal to an average curvature contribution for all thescribe line locations.

In an alternative embodiment of the present method, each installment hasthe same steps of measuring, determining and scribing, but eachinstallment changes the curvature to an intermediate target curvature.The intermediate target curvatures are predetermined. In a process usingthree installments, for example, there will be two intermediate targetcurvatures. The target curvature for the third and final installment isthe final target curvature. Scribe lines are scribed at thepredetermined scribe line locations.

The present invention also includes a method for providing a desiredcurvature change in an ABS surface of a slider. The method includes thesteps of establishing scribe line locations on the back surface of theslider. The scribe line locations are sufficiently spaced apart suchthat neighboring scribe lines at neighboring scribe line locations actindependently. Next, a curvature contribution for each scribe linelocation is determined. Next, scribe line locations are selected suchthat a sum of the curvature contributions of the selected locations isequal to the desired curvature change. Finally, scribe lines are scribedat the selected locations.

Preferably, the scribe line locations are spaced apart by a distancesufficient to ensure that neighboring scribe lines at neighboringlocations act independently.

Also preferably, scribe line locations are selected such that theaverage curvature change per scribe line is substantially equal to anaverage curvature contribution for all scribe line locations.

All methods of the present invention can be applied to both crowncurvature and camber curvature.

DESCRIPTION OF THE FIGURES

FIG. 1 (prior art) shows a close-up view of a slider in operationreading/writing data to a magnetic data storage disk.

FIG. 2A shows an example of a slider with negative crown curvature.

FIG. 2B shows an example of a slider with positive crown curvature.

FIG. 3A shows an example of a slider with negative camber curvature.

FIG. 3B shows an example of a slider with positive camber curvature.

FIG. 4 shows how the measurement of curvature is defined in the presentinvention.

FIG. 5 shows an air bearing surface (ABS) of the slider.

FIG. 6A shows an apparatus according to the present invention which canmeasure the curvature of the ABS.

FIG. 6B shows four points on the ABS used by the apparatus of FIG. 6A tomeasure curvature-two points for crown curvature, and two points forcamber curvature.

FIG. 6C shows the output of a position sensing detector in the apparatusof FIG. 6A when lasers beams are alternately pulsed.

FIG. 7A shows another apparatus according to the present invention whichcan measure the curvature of the ABS.

FIG. 7B shows scan lines on the ABS used by the apparatus of FIG. 7A tomeasure crown curvature and camber curvature.

FIG. 8 shows a table illustrating the signals produced by the apparatusof FIG. 7A for different curvatures of the ABS.

FIG. 9 shows a curvature adjustment tool which can adjust the curvatureof sliders still attached in row form.

FIG. 10 shows an exemplary distribution curve of initial curvatures ofdifferent sliders in relation to a final target curvature.

FIG. 11 shows a graph of different curvatures of a particular row ofsliders.

FIG. 12 shows how the curvature of a particular slider changes whilebeing processed through installments in the method of the invention.

FIG. 13 shows the curvature distribution of a group of sliders beforeand after being processed.

FIG. 14A shows a back surface of a slider scribed according to thepresent invention. FIG. 14A is physically aligned with FIG. 14B.

FIG. 14B shows a graph illustrating how the effect on curvature providedby a crown scribe line depends upon the crown scribe line location.

FIG. 15 shows a graph illustrating how two scribe lines located closetogether affect the net result on slider curvature.

FIG. 16 shows the back surface of a slider with scribe line locationsoutlined.

FIG. 17 shows a graph illustrating how to select scribe line locationsto achieve a desired curvature change.

FIG. 18 illustrates the preferred method of the present invention inwhich a predetermined percentage of a measured curvature difference iscorrected for in each installment.

FIG. 19 is a flow chart illustrating a preferred method of repeatedlyadjusting slider curvature by installments based on percentages.

FIG. 20 is a flow chart illustrating a second method of repeatedlyadjusting slider curvature by installments based on achievingintermediate target curvatures.

FIG. 21 shows a back surface of a slider having crown scribe lines whichprovide a desired crown curvature.

FIG. 22 shows a back surface of a slider having camber scribe lineswhich provide a desired camber curvature.

FIG. 23 shows a graph illustrating how the effect on curvature providedby a camber scribe line depends upon the camber scribe line location.

FIG. 24 shows a slider which has both crown scribe lines and camberscribe lines.

FIGS. 25A and 25B show sliders which have herringbone scribe lines thataffect both crown and camber curvature.

FIG. 26 shows a back surface of a slider which has angled scribe linesthat affect both crown curvature and camber curvature.

FIG. 27 shows a back surface of a row which has crown scribe lines.

DETAILED DESCRIPTION

The present invention provides a method for adjusting the curvature ofmagnetic sliders used for transducers in data storage hard drives.

FIG. 1 shows a close-up side view of a slider 20 held above a hard drivedisk 22 which is moving in the direction of the arrow 24. The slider 20has an air bearing surface (ABS) 26 facing the disk 22. The slider alsohas a back surface 28. The slider 20 is inclined with respect to thedisk 22 so that air moving along with the disk provides aerodynamic liftto the slider 20. For reliable operation and maximum data storage in ahard drive, a fly height 30 should be small, stable, and well defined.The shape and curvature of the air bearing surface 26 is very importantfor determining the fly height 30.

The shape of the air bearing surface 26 is described in terms of twotypes of curvature, crown and camber. FIG. 2A shows a side view of aslider which has a concave air bearing surface 26 which appears curvedwhen viewed from the side. The slider is said to have negative crown.Negative crown is caused by residual stress in the slider, which isoften a result of lapping the ABS. Negative crown is generallyundesirable for air bearing surfaces. FIG. 2B shows a slider 20 havingan ABS with positive crown. A small value of positive crown is generallydesirable for air bearing surfaces 26. An ABS with a small, positivevalue of crown provides a more stable and predictable fly height 30.

It is noted that it is the average curvature of the ABS 26 which isimportant. Therefore, the curvature can be expressed as a single numberindicating the average curvature. The exact shape of the curvature doesnot have a significant effect upon fly height 30, provided that theaverage curvature is a well-defined value. The fly height 30 isapproximately proportional to the average curvature. For example, atypical fly height sensitivity is about 0.25 nanometers of fly height 30change for each nanometer of crown curvature change.

FIG. 3A shows a front view of a slider 20 with a curved ABS whichappears curved when viewed from the front (i.e. in the direction of thearrow 24). The disk 22 is moving into the page. The slider is said tohave negative camber. Negative camber is generally undesirable for airbearing surfaces because the ABS is more likely to contact the disk.FIG. 3B shows a slider having positive camber. A small value of positivecamber is generally desirable for air bearing surfaces 26. An ABS with asmall, positive value of camber curvature provides a more stable andpredictable fly height 30.

FIG. 4 shows how crown and camber (most generally, curvature) ismeasured in the present invention. Curvature is measured in units ofdistance defined by the length 32. Length 32 is the distance between thehighest and lowest points on the ABS 26. A negative curvature valueindicates that the ABS is concave; a positive curvature value indicatesthat the ABS is convex (this is true for both crown and cambercurvature). Length 32 is either the crown curvature or camber curvature,depending upon the orientation of the slider 20.

FIG. 5 shows a close-up view of the slider ABS. The ABS 26 does notextend over an entire bottom surface 34 of the slider 20. Portions 36 ofthe bottom surface of the slider are recessed and therefore do notsubstantially affect the fly height 30. The ABS 26 is polished andraised above the remaining portions 36. Therefore, when measuringcurvature, it is only necessary to measure the curvature of the ABS 26and not the portions 36.

FIG. 6A shows an apparatus according to the present invention formeasuring the curvature of the ABS 26. Two lasers 40, 42 supply laserbeams 43 a, 43 b to a first beamsplitter 44. The lasers 40, 42 andbeamsplitter are located so that the beams after having passed throughthe beamsplitter 44 are spaced apart by a distance 46 and parallel. Theslider 20 whose curvature is to be measured is placed a distance awayfrom the beamsplitter 44 in the path of the laser beams 43 a, 43 b. Alens 45 is located in front of the slider 20. The beams 43 a, 43 b areincident upon the ABS 26 at two spaced apart points 47, 48. Theapparatus measures the curvature between the points 47, 48. FIG. 6Bshows a top view of the ABS 26 which shows where the points 47, 48 arelocated on the ABS 26. Of course, the points 47, 48 can be locatedanywhere on the ABS 26 where a curvature measurement is required. Ifcamber curvature is being measured, then the beams will be incident uponthe ABS 26 at locations 63, 65 (i.e. horizontally spaced apartlocations). The beams 43 a, 43 b reflect from the ABS 26 and enter asecond beamsplitter 50 which directs the reflected beams to a positionsensing detector 52. The beams are incident on the detector 52 at spacedapart points 53, 54. The distance between the points 53, 54 determinesthe output of the detector 52 and is indicative of the curvature of theABS 26.

Preferably, the optical path length from the ABS to the detector (i.e.from point 47 to point 53, and from point 48 to point 54) is in therange of about 25-300 millimeters.

Preferably, the second beamsplitter 50 is a polarizing beamsplitter anda quarter-wave plate 51 is located between the second beamsplitter 50and ABS 26. Proper alignment between the polarizing beamsplitter 50 andquarter-wave plate assures that all the light reflected from the ABS isdirected toward the detector 52.

It is noted that the slider 20 may be made of a composite ceramicmaterial having a predetermined grain size (e.g. TiC and Aluminacomposite ceramics). The beam spot sizes at locations 47 and 48 must belarge compared to the grain size in order to obtain accurate curvaturemeasurements. The beam spot sizes should also be small enough to providesufficient spatial resolution.

If the ABS 26 is flat, then the distance between points 47 and 48 is thesame as the distance between points 53 and 54. If the ABS 26 is concave(but not excessively concave), then the distance 47-48 will be greaterthan the distance 53-54. If the ABS 26 is convex, then the distance47-48 will be less than the distance 53-54. Therefore, the apparatusshown can measure positive and negative curvature between any two pointson the ABS 26. By appropriately orienting the beams 43 a, 43 b withrespect to the slider 20, both crown and camber of the slider 20 can bemeasured.

In operation, beams 43 a and 43 b are alternately pulsed such that onlyone beam is on at a time. Preferably, the lasers 40, 42 are diode lasersand are alternately switched. This produces an output from the detector52 shown in FIG. 6C. The output can be described as being a DC-biasedsquare wave signal. The voltage step difference (V₂-V₁) is proportionalto the distance between points 53 and 54, which provides a measure ofthe curvature of the ABS 26. In a particular embodiment the lasers arepulsed at a rate of about 100 kHz. If each curvature measurement isaveraged over 10 cycles, then a curvature measurement is provided every100 microseconds. Preferably, a lock-in amplifier tuned to the frequencyof the pulsed lasers 40, 42 (i.e. 100 kHz in the above example) is usedto measure the voltage step difference. Alternatively, an RMS voltagemeter is used to measure the voltage step difference.

The accuracy of the measurements depends upon the total distancetraversed by the beams after being reflected from the ABS 26. Typically,the optical path length between points 47 and 53 is about 25 to 300millimeters. An apparatus according to the present invention can measurecurvature to within 1 nanometer.

FIG. 7A shows another embodiment of the present invention for measuringthe crown and camber curvature of the ABS 26. A laser 54 directs a laserbeam 56 towards a scanner 58. The scanner 58 can be a scanning mirror oran acousto-optical scanner, for example. The scanner may scan the laserbeam 56 in one or two dimensions. The scanner directs the beam 56through a beamsplitter 60 and through a scan lens 62. The scan lens 62is one focal length away from the beam pivot scan point 61. The slider20 is located behind the lens 62. The beam 56 strikes the ABS 26substantially perpendicularly.

The beamsplitter 60 directs a reflected beam from the ABS 26 towards theposition sensing detector 52. The detector 52 is preferably located asfar away as possible from a scan lens focal plane 67 of the lens 62 suchthat the reflected beam is always incident upon the detector 52.Typically, the distance between focal plane 67 and detector 52 is in therange of about 1-3 millimeters. This assures that there will be anoscillatory signal from the detector for many different values ofcurvature. In FIG. 7A, the detector is shown located in front of thefocal plane 67 (i.e. between the beamsplitter 60 and focal plane 67),however, the detector can also be located behind the focal plane 67.

Alternatively, the detector 52 is located one focal length from the lens62 so that the surface of the detector is coincident with the focalplane 67. In this case, if the ABS 26 is flat, then the beam will alwaysbe incident upon the same point of the detector 52 as the beam isscanned and no oscillatory signal is produced. The amplitude of thesignal from the detector indicates the magnitude of curvature, and thephase of the signal indicates whether the curvature is positive ornegative (i.e. convex or concave).

FIG. 7B shows a top view of the ABS 26 showing a beam trajectory 66 overthe ABS 26. The beam trajectory 66 is the path over which the beam 56moves as the scanner operates. The beam trajectory shown in FIG. 7B is astraight line, but curved trajectories can also be used. The trajectory66 shown would be used to measure crown curvature. An orthogonaltrajectory 64 would be used to measure camber curvature. Of course, withappropriate control of the scanner, both crown and camber curvature ofthe slider 20 can be measured.

The detector 52 preferably is in communication with a phase sensitivesignal receiver 68 such as a lock-in amplifier referenced at the scanfrequency of the scanner. The position of the scanner is continuouslymonitored by the signal receiver 68 as a phase reference 69. Theamplitude of the signal from the detector 52 indicates the magnitude anddirection of curvature (i.e. convex or concave). This is shown in thetable of FIG. 8. The lock-in amplifier 68 can sensitively detect changesin phase and magnitude of the detector signal, and therefore provideaccurate curvature measurements. The table of FIG. 8 assumes that thelaser beam is scanned sinusoidally across the ABS.

The use of a lock-in amplifier also provides fast measurements. If thebeam is scanned at a frequency of about 1500 Hz, and the integrationtime of the lock-in amplifier is set for 3 milliseconds, then each newmeasurement averages over 5 round trips of the laser beam. Approximately300 separate curvature measurements can be performed per second. Bycomparison, an interferometric measurement according to prior arttechniques typically requires about 5 to 15 seconds to complete.

In certain applications of the apparatus of FIG. 7A, it is desirable toscan the laser beam such that the beam trajectory 66 extends overremaining portions 36. This is necessary, for example, if the ABS 26includes disconnected regions. However, while the beam is incident uponthe remaining portion 36, the signal from the detector is not ofinterest because the remaining portion 36 is expressly not part of theABS 26. Therefore, for the period of time during which the beam isdirected toward the portion 36, the signal from the detector should beignored. The signal from the detector is only useful while the beam isstriking the ABS 26. In a preferred implementation, the signal from thedetector is replaced with a signal from a sample-and-hold circuit 71during times when the beam is directed toward the portion 36. Thesample-and-hold circuit provides to the computer the most recent signalfrom the detector before the beam is moved off of the ABS 26.

The present invention includes a method of scribing sliders 20. Themethod can be practiced with the apparatus disclosed in U.S. Pat. No.5,266,769 to Deshpande. FIG. 9 shows an apparatus capable of performingthe present slider scribing method on a monolithic row 69 of sliders 20(here seen edge-on). The apparatus has a curvature measuring tool 70such as the apparatus of FIG. 7A. The curvature measuring tool is incommunication with a computer 72 which controls a laser scribing tool74. The laser scribing tool produces a scribing beam 76 which is capableof ablating material from the back surface 28 of the sliders 20. Ascanner 78 such as a mirror, XY-galvo scanner or acousto-optical scannerguides the scribing beam 76 over the back surface of the slider 20. Therow 69 of sliders can be moved so that the curvature measuring tool 70and scribing tool 74 can access all the sliders 20 in the row 69, one ata time. The curvature measuring tool 70 measures the curvature of eachslider 20 individually. The scribing tool 74 scribes each sliderindividually. Therefore, although the sliders are still attached in rowform, each slider is processed individually. Most sliders are orientedin the row 69 such that crown curvature is primarily adjusted byscribing crown scribe lines in the direction of arrow 99 (parallel withthe long dimension of the row) , and camber curvature is primarilyadjusted by scribing camber scribe lines in a direction in and out ofthe page (perpendicular with the long dimension of the row).

More generally, crown scribe lines extend over the back surface in adirection perpendicular with the intended direction of air flow over theABS, and camber scribe lines extend over the back surface in a directionparallel with the intended direction of air flow over the ABS. Crownscribe lines and camber scribe lines do not produce exclusive effects.Crown scribe lines also tend to increase camber curvature, and camberscribe lines also tend to increase crown curvature.

It is noted that the curvature measuring tool 70 is preferably theapparatus of FIG. 7A, and preferably uses a phase sensitive receiversuch as a lock-in amplifier 68. The laser scribing tool 74 can have manydifferent kinds of scribing lasers. For example, the scribing tool 74can have a pulsed 1.064 micron YAG laser. In a particular embodiment, a1.064 micron Nd:Vanadate laser provides, on average, about 2 watts ofoptical power in the form of a 20-110 kHz pulse train where each pulsehas a duration in the range of 5-500nanoseconds, more preferably 10-100nanoseconds (YAG lasers can also be used). It is undesirable to use acontinuous (cw) laser because the resulting scribe lines will be toodeep and the sliders will be heated excessively. Of course, mechanicalscribers or micro-sandblasting tools can be substituted for the laserscribing tool 74. This is not preferred, however, because laser scribingtools tend to be faster and produce more accurate scribe lines. Also,mechanical scribing tools and microsandblasters are undesired becausethey increase curvature only if they are directed at the ABS side of theslider. Therefore, such tools must be operated alternately with thecurvature measurement tool, preventing simultaneous scribing andcurvature measurement.

The scribe lines can have a broad range of depths, from sub-micron (e.g.surface roughening) to tens of microns. However, excessively deepscribing tends to produce large amounts of particulate contamination,which can damage the sliders. Preferably, the scribe lines are in therange of 0.2-4 microns deep, and most preferably about 1 micron deep.

An object of the present invention is to provide all the sliders 20 withthe same ABS curvature with little error. This desired curvature istermed the final target curvature. In operation, the curvature measuringtool 70 determines an initial curvature of each slider in the row 69.The curvature measurement for each slider 20 is sent to the computer 72.The computer determines a scribing pattern that, when scribed on theback surface 28 of each slider 20, changes the curvature of each slider.The curvature of each slider is changed to an intermediate value betweenthe initial curvature and the final target curvature. Themeasurement/scribing process is repeated until the final targetcurvature is reached. Each slider 20 in the row 69 typically has adifferent initial curvature, and so requires a different pattern ofscribe lines. The method by which the computer 72 determines the patternof scribe lines for each slider is the subject of the present invention.

When manufactured, each slider 20 typically has an inaccurately definednegative crown (i.e. the ABS surface is concave). However, for optimalfly height, it is best for the crown curvature to be slightly positivewith little error. FIG. 10 shows a typical distribution plot of initialcrown curvature 78 for sliders when they are first manufactured. Asimilar plot can be made for camber curvature. The distribution 78 isrelatively broad and centered at a negative value of about −5nanometers. For best flying characteristics, the ABS 26 of the slidersshould have a well-defined final target curvature 80 (the desiredcurvature), which in this example is about +25 nanometers. The finaltarget curvature 80 depends upon the design of the ABS 26, among otherfactors. It can be seen that the method of curvature adjustment mustincrease the curvature to a positive value and also decrease thestandard deviation of the curvature distribution.

It is noted that the method of scribing the back surface 28 can onlyincrease the curvature. The curvature change produced by removingmaterial from the back surface 28 only goes in one direction. Therefore,if the final target curvature 80 is substantially exceeded, then theslider requires a substantial amount of additional processing with amechanical scriber or macrosandblaster to reduce the curvature.

It is noted that, although the following methods are discussed mainly interms of crown curvature, the methods of the present invention applyequally well to adjusting camber curvature.

In a first step of the present method, the crown curvature of eachslider 20 in the row 69 is measured. This measurement preferablyprovides a measurement of the average curvature of the ABS 26. FIG. 11shows an example of a set of average crown curvature measurements from arow 69 having 10 sliders 20. Next, a difference 82 between the initial,measured curvature 81, and the final target curvature 80 is determinedfor each slider.

In the present method it is strongly preferred for the entire difference82 to be corrected in several steps (installments). This is because theprocess of increasing the curvature (i.e. scribing) is irreversible andthe final target curvature 80 must not be exceeded. Therefore, thepresent method includes the process of repeatedly measuring thecurvature 81, correcting a portion of the difference 82, and thenrepeating the measurement/scribing steps. The steps of measuring thecurvature and scribing the lines are performed repeatedly. This processassures that the final target curvature 80 is not exceeded and that thefinal curvature of the slider is fairly accurate. The accuracy of thefinal curvature of the slider will depend upon, among other factors, howmany measurement/scribing cycles (i.e. installments) are used for eachslider.

FIG. 12 shows a graph of the average crown curvature (i.e. averaged overthe ABS) of a single slider at several installment stages during aprocess including three installments. The initial curvature of theslider 81 is measured and the difference 82 is determined as describedabove. A portion of the difference 82 is corrected for by a firstinstallment 85 which includes scribing the back surface 28. After thefirst installment 85, the curvature is measured again and a secondcurvature 86 is found and a new difference 87 is determined. In a secondinstallment 88, a portion of the new difference 87 is corrected toproduce a third curvature 89. This process is repeated as many times asdesired until the final target curvature 80 is achieved. Moreinstallments can generally provide sliders having more accuratelydefined curvature. Typically, 2-3 installments are sufficient for thesliders to achieve a curvature which is within about 1 nanometer of thefinal target curvature 80.

FIG. 13 shows curvature distributions for sliders before 90 and after 91curvature adjustment according to the present invention. The method ofthe present invention changes slider curvature to the final targetcurvature and simultaneously reduces the standard deviation of slidercurvature distribution.

An essential part of the present invention is the method used todetermine the number and distribution of scribe lines necessary for adesired curvature change. For each slider during each installation, thenumber and distribution of scribe lines for the desired curvature changemust be determined. The effect of a scribe line on the average curvatureof the slider is dependent upon its location on the slider. FIG. 14Ashows the back surface 28 of a single slider 20 with crown scribe lines100 (i.e. scribe lines that primarily affect crown curvature, althoughthey also affect camber curvature). Camber scribe lines (not shown) havean orthogonal orientation. Crown scribe lines 100 are oriented in adirection perpendicular to the direction of the disk motion 102. Thegraph of FIG. 14B illustrates the effect of crown scribe line locationon curvature change. Scribe lines near a middle 104 of the slider havethe greatest effect on curvature, almost 1.5 nanometers of curvaturechange for a single line (for this particular example). Scribe linesnear leading edge 106A and trailing edge 106B of the slider 20 have verylittle or no effect on curvature. The graph of FIG. 14B can bedetermined empirically for any desired slider design. Also, a graphanalogous to FIG. 14B can be made for camber scribe lines. It is notedthat trailing edge 106B has delicate magnetic sensors for interactingwith the magnetic data storage medium. The magnetic sensors can bedamaged by the heat produced by scribing lines. For this reason it isnecessary to establish a margin 107 within which no scribe lines may bescribed. For typical sliders, margin 107 may have a width of about 150microns. A margin 109 may also exist at the leading edge 106A becausescribe lines near the edges 106A, 106B are ineffective at changingcurvature.

The graph of FIG. 14B assumes that there is only a single scribe line onthe slider 20. Scribe lines located close together do not behaveindependently to affect curvature, but rather have reducedeffectiveness. FIG. 15 illustrates this point. Shown in FIG. 15 is agraph of curvature change for scribing an additional scribe line on aslider already having a scribe line at a location 108 (a graph analogousto FIG. 15 can be made for camber curvature). It can be seen from thisgraph that, since there is already a scribe line at location 108,scribing another line close to location 108 will have a reduced effecton the ABS curvature. A range 110 is shown within which a scribe linehas a diminished effect upon curvature. The range 110 depends upon thedepth of the scribe line at location 108 and the mechanicalcharacteristics of the slider. For typical sliders which are about300-400 microns thick with scribe lines about 2 microns deep, the range110 is about 35-55 microns. Placing a second scribe line within range110 results in the second scribe line having a greatly reduced effectupon curvature. Placing scribe lines outside of range 110 results in thescribe lines acting independently to affect curvature. The range 110therefore approximately determines the maximum number of independentlyacting scribe lines which can fit onto a slider. For example, for crowncurvature-affecting scribe lines, if a slider is 2000 microns long(length in the direction of air flow), the range 110 is about 50microns, and margins 107, 109 are each 200 microns wide, then about2000-400/50+1=33 independently acting crown scribe lines can fit on theslider. This maximum number of independent scribe lines determines a setof possible scribe line locations 112, shown in FIG. 16. The locations112 are spaced apart by a distance 111 sufficient to ensure thatneighboring scribe lines 112 act independently. A scribe line may or maynot be scribed at each location 112. However, all scribe lines must belocated at the predetermined locations 112.

Distance 111 can be in the range of about 5-200 microns, but ispreferably in the range of about 20-80 microns, and is more preferablyin the range of about 35-55 microns. These distances are applicable toboth crown scribe lines and camber scribe lines.

An average curvature contribution 105 for all scribe line locations 112is shown in FIG. 17. The average curvature contribution 105 is theaverage curvature change per scribe line for all the scribe linelocations 112. The significance of the average curvature contribution105 is discussed below.

In the present invention, each installment of scribe lines is performedby selecting which scribe line locations 112 are to receive scribelines. In each installment, the scribe lines 100 are distributed on thesurface of the slider such that the average curvature change per scribeline (i.e. per scribe line that is actually scribed) is equal to theaverage curvature contribution 105 of all scribe line locations. Thisrequirement ensures that the scribe lines are dispersed (i.e. notbunched together). In other words, if scribe lines are scribed near themiddle of the slider (where the effect of a scribe line is greatest),then other scribe lines must be scribed near the periphery (i.e. nearedges 106).

FIG. 17 shows a graph which can be used to determine which scribe linelocations should receive scribe lines in a particular installment. Thegraph allows one to determine what effect each possible scribe linelocation 112 has on curvature. Each scribe line location 112 has anassociated curvature contribution. For example, scribe line 112-1 has acurvature contribution of about 1.2 nm, scribe line 112-2 has acurvature contribution of about 0.62 nm, and scribe line 112-3 has acurvature contribution of about 1.0 nm. By adding up the curvaturecontributions of the individual scribe lines, the total curvature changecan be predicted. For example, scribing lines 112-1, 112-2 and 112-3will produce a curvature change of about 1.2+0.62+1.0=2.82 nm. Thescribe line locations 112 are located far enough apart 117 so that theyact independently and do not diminish each others effect on curvature.

Scribe lines 112-1, 112-2, and 112-3 approximately satisfy the averagecurvature change per scribe line requirement described above. Theaverage curvature change for 112-1, 112-2, and 112-3 is 2.82 nm/3lines=0.94 nm/line. This is rather close to the average curvaturecontribution for all scribe line locations 105, which is 1.0 nm perline. Equalizing the average curvature change and the average curvaturecontribution for all scribe line locations necessarily results in thescribe lines being dispersed over the back surface 28 of the slider.

Preferably, each installment of scribe lines is selected to compensatefor a predetermined percentage of the initial curvature difference. Thisprocess is illustrated in FIG. 18, which illustrates the method in a3-installment process. The initial curvature 81 is measured for eachslider and the initial curvature difference 82 is determined between theinitial and final target curvature 80. Intermediate percentages are thenselected. The intermediate percentages determine what percentage of theinitial curvature difference 82 is corrected for in each installment. Ina particular exemplary embodiment, the intermediate percentages are 60%and 90%. This establishes a first intermediate percentage target 86 anda second intermediate percentage target 89. Targets 86, 89 are definedas being located a predetermined percentage distance from the initialcurvature 81 and the final target curvature 80. In the 60-90 embodiment,the first intermediate percentage target 86 is 60% of the initialcurvature difference (i.e. length 92 is 60% of length 82); and thesecond intermediate percentage target 89 is 90% of the initial curvaturedifference (i.e. length 94 is 90% of length 82). Each slider in a groupmay have different targets 86, 89 depending upon the initial curvature81.

In the first installment, lines are scribed to achieve the firstintermediate percentage target curvature 86. Then, in the secondinstallment, the curvature is remeasured, and lines are scribed to reachthe second intermediate percentage target curvature 89. Finally, in thethird installment, lines are scribed to reach the final target curvature80. Preferably, the intermediate percentages (i.e. 60% and 90%) areselected such that only 1-3 scribe lines are required in the finalinstallment. If more installments are desired, then more intermediatepercentages must be specified (e.g., for 5installments, 4 intermediatepercentages are necessary). An advantage of this process is that itassures that every slider is processed through the predetermined numberof installments, regardless of a slider's initial curvature.

It is noted that when scribing a number of sliders, each slider may havedifferent intermediate percentage targets 86, 89, depending on theinitial curvature 81. It is the intermediate percentages (i.e. ratio ofdifference 92 to difference 82 (60% in example above), and ratio ofdifference 94 to difference 82 (90% in example above)) which are thesame between different sliders being processed according to this method.

As a specific, single-slider example, if a slider has an initialcurvature of -15 nm and the final target curvature is +15 nm, then theinitial curvature difference is +30 nm. The first installment isdesigned to correct for 60% of this curvature difference to bring theslider to a curvature of +3 nm. Next, the second installment correctsfor 90% of the initial curvature difference to bring the slider to acurvature of +12 nm. In a third and final installment, 100% of theinitial curvature difference is corrected for to bring the slidercurvature to +15 nm. A flow chart illustrating the method of thispreferred embodiment is shown in FIG. 19.

It is noted that the intermediate percentages can have a wide range ofvalues. In a process with three installments, the first intermediatepercentage can be in the range of about 40-95%, and the secondintermediate percentage can be in the range of about 60-99%. Morepreferably, for a process with three installments, the firstintermediate percentage is in the range of 60-80%, and the secondintermediate percentage is in the range of 75-95%. For a process withtwo installments (and hence only one intermediate percentage targetcurvature), the intermediate percentage is preferably in the range of70-90%.

In an alternative embodiment, each installment of scribe lines isdesigned to produce a predetermined intermediate target curvature ineach slider. Each intermediate target curvature is between the initialcurvature and the final target curvature. For example, consider a finaltarget curvature of +15 nm and a group of sliders with an averageinitial curvature of −15 nm. A first intermediate curvature may be setat +5 nm, and a second intermediate curvature may be set at +12 nm. Inthe first installment, the curvature is measured and lines are scribedto produce the first intermediate curvature. Then, the curvature isremeasured, and a curvature difference between the measured curvatureand the second intermediate target curvature is determined. Then, linesare scribed to produce the second intermediate curvature. Then, thecurvature is measured again, and lines are scribed in the finalinstallment to produce the final target curvature. Preferably, theintermediate target curvatures are selected such that only 1-3 scribelines are necessary in the final installment. The intermediate targetcurvatures and number of installments may be selected empirically, andwill depend upon the design of the sliders. A flow chart illustratingthe process is shown in FIG. 20.

Therefore, in the present invention, there exist two methods ofdistributing the curvature adjustment among the installment steps. Themethods of FIG. 19 and FIG. 20 are specific examples of curvatureadjustment by repeatedly measuring and changing the slider curvature.The first method of FIG. 19 corrects for a predetermined percent of theinitial curvature difference with each installment. The second method ofFIG. 20 corrects for a predetermined amount of the curvature differencewith each installment. In both methods, it is preferred to distributethe necessary curvature adjustment among the installments so that thefinal installment requires only 1-3 scribe lines. Minimizing the numberof scribe lines needed in the final installment improves the accuracy ofthe process.

The methods of FIG. 19 and 20 are performed on individual sliders. Theindividual sliders may or may not be attached in row form, as shown inFIG. 9. The curvature of individual sliders can be separately adjustedeven though the sliders are attached in row form.

Generally, any number of installments will work with either method(methods of FIGS. 19 and 20). If a large number of installments is used(by correcting a small amount of curvature in each installment), thesliders will have a more accurate curvature, but will require more timeto process. More installment steps are necessary for sliders having acurvature which is far from the final target curvature, or for groups ofsliders which have large deviation (range) of initial curvature values.For many applications, 3 installments are sufficient.

The method of curvature adjustment by repeatedly adjusting slidercurvature in installments is preferably applied to sliders stillattached in row form, as shown in FIG. 9. Each curvature measurement andscribing process is performed individually on each slider in the row.

It is noted that scribing a slider heats the slider. Heating cantemporarily change the curvature of the slider. In the present inventionit is preferred to allow the sliders to cool to the ambient temperaturebetween installments. If the sliders are not allowed to cool adequately,then incorrect curvature measurements are produced and the sliders willhave inaccurate curvature. Typically, 30 seconds or longer betweeninstallments is adequate. In a particularly preferred embodiment, anentire row of sliders is processed through one installment. Then, theentire row is allowed to cool before being processed through the nextinstallment. Sufficient cooling time can be provided by loading many(e.g. about 10) slider rows into the scribing apparatus. A scribedslider row is allowed to cool while the other slider rows are beingscribed. This method maximizes throughput while maintaining curvatureaccuracy.

FIG. 21 shows the back surface 28 of a slider 20 which has been scribedaccording to the present invention to change crown curvature. The arrow102 indicates the direction of disk motion (and air motion) over the airbearing surface 26 (the surface opposite the back surface 28) of theslider. The slider 20 has scribe lines 100 which extend a full width 120of the slider. The slider also has a single partial scribe line 118which does not extend the full width 120. Each slider 20 in a slider rowwill generally have a different pattern of scribe lines 100 and partialscribe lines 118. This is because, for most slider rows, each slider hasa different initial curvature and therefore needs a different number anddistribution of scribe lines to reach the final target curvature.

In all the installments except for the final installment, it ispreferable that all lines scribed extend a full width 120 of the slider.In the final installment, a single partial scribe line 118 can bescribed if a full scribe line cannot be found which matches thecurvature change required. A partial scribe line can be formed byplacing a fast shutter (e.g. a fast electromechanical shutter with aopen/shut time of less than about 1 millisecond) in the path of thescribing laser beam and closing the shutter at appropriate times duringthe scan of the scribing laser. The curvature effect from partial scribelines is approximately proportional to the length of the line. Consider,for example, a case where a scribe line location having a curvaturecontribution of 1.5 nm is available (i.e. unscribed) for the finalinstallment, but only 0.75 nm of curvature change is needed. Scribing apartial scribe line having half the full width 120 provides the desired0.75 nm of curvature. The present invention includes individual sliderswith partial scribe lines 118 which do not extend the entire width 120of the slider 20. Preferably, partial scribe lines are symmetricallylocated about a crown centerline 125. When scribed according to thepresent method, sliders will almost never have more than a singlepartial scribe line. This is because partial scribe lines are only usedwhen full scribe lines cannot generate the required amount of curvaturechange in the final installment. Most sliders will have a single partialscribe line, however.

Although the present invention has been described mainly in terms ofadjusting crown curvature, the methods of the present invention applyequally well to adjusting camber curvature. For example, the installmentmethods illustrated in FIGS. 19 and 20 apply equally well when adjustingcamber curvature. FIG. 22 shows the back surface of a slider which hasbeen scribed to adjust camber curvature. Camber scribe lines 130 areoriented in a direction parallel with the disk and air motion 102.Camber scribe lines 130 primarily affect camber curvature, although theyalso have an effect upon crown curvature. Margins 107, 109 prevent thecamber scribe lines 130 from extending the entire width of the slider.Preferably, margins 107, 109 have the same width so that camber scribelines are symmetrically located about a camber centerline 132.Symmetrically locating camber scribe lines 130 about the cambercenterline 132 assures that the camber scribe lines provide a uniformcamber curvature change across the slider. It is noted that camberscribe lines 130 have very little effect on camber curvature whenlocated near sides 134, and have a large effect on camber curvature whenlocated near centerline 125. Camber scribe lines 130 are located inpredetermined locations which are spaced apart a distance sufficient toensure that neighboring camber scribe lines act independently. Partialcamber scribe lines 133 can also be used. Partial camber scribe linesare designed and produced in the same manner as partial crown scribelines.

FIG. 23 shows a graph of camber curvature change per scribe line vs.camber scribe line location. The graph is analogous to the graphs ofFIG. 14B and FIG. 17. The graph of FIG. 23 is used in the same mannerdiscussed above to determine which predetermined scribe line locationsshould receive camber scribe lines. Line 138 indicates the averagecamber curvature change for all possible camber scribe lines. Line 136in FIGS. 22 and 23 shows the direction in which the graph is drawn. Line132 indicates the location of the camber centerline 132 of FIG. 22. Themethod of locating camber scribe lines is substantially the same as themethod discussed in terms of crown curvature.

FIG. 24 shows a slider which has a rectangular grid of scribe lines forcorrecting both crown and camber curvature. Crown curvature and cambercurvature adjustments can be performed jointly.

FIG. 25A shows a slider with herringbone scribe lines 140. Theherringbone pattern is centered upon centerline 142. Herringbone scribelines affect both crown and camber curvature. A scribe angle 144determines how much the herringbone scribe lines affect crown and howmuch they affect camber. If the scribe angle 144 is small (i.e. about 0degrees), then the herringbone scribe lines 140 primarily affect crowncurvature. A 0 degree herringbone scribe line is equivalent to a crownscribe line. If the scribe angle 144 is large (i.e. about 90 degrees),then the herringbone scribe lines primarily affect camber curvature. A90 degree herringbone scribe line is equivalent to a camber scribe line.Herringbone scribe lines can be made having different orientations. FIG.25B shows a slider with rotated herringbone scribe lines 146 that arerotated 90 degrees compared to the herringbone scribe lines of FIG. 25A.The rotated herringbone scribe lines 146 are centered about a centerline148. Rotated herringbone scribe lines 146 have the same effect on crownand camber curvature as herringbone scribe lines 140. Scribe angle 150determines the relative effect on crown and camber curvature. Scribelines 140 and 146 can also rotated 180 degrees compared to theorientations shown (i.e. herringbone scribe lines 140 may also point tothe left, and herringbone scribe lines 146 may also point up). It isnoted that partial herringbone scribe lines can be used. FIG. 25A showsa partial herringbone scribe line 145.

FIG. 26 shows the back surface of a slider having angled scribe lines160. Angles scribe lines 160 are used to simultaneously adjust crown andcamber curvature. Angle 162 determines the relative effectiveness thescribe lines have in changing crown curvature and camber curvature. Ifangle 162 is about 0 degrees, then the scribe lines 160 primarily effectcamber curvature. If the angle 162 is 90 degrees, then the scribe lines160 primarily effect crown curvature. Angle 162 is measured from acenterline 164 which is parallel with the intended direction 102 of airflow over the air bearing surface.

As shown in FIG. 9, the present invention can be used to individuallyscribe sliders still attached in row form. FIG. 27 shows the backsurface of 6 monolithically integrated (i.e. made of a single piece ofmaterial) sliders 20 still attached in row form which have been scribedaccording to the present invention. The length 128 of the row isperpendicular to the intended direction of air flow over the ABS. Thescribe lines 100, and partial scribe lines 118 on individual sliders 20can be considered to be portions of row-length crown scribe lines whichextend the whole length 128 of the row. This is because the scribe linelocations 112 are in the same corresponding locations on differentsliders in the row. Box 126 contains a row-length crown scribe line. Thepresent invention includes slider rows which have row-length crownscribe lines (e.g. row-length crown scribe line within box 126) which donot extend the entire length 128 of row. The row-length scribe lineterminates at boundaries 122 between sliders where partial scribe lines118 exist, or where neighboring sliders do not have a scribe line atall. The row-length scribe line in the box 126 is discontinuous acrossthe length 128 of the row. Most sliders have a single partial scribeline 118.

It will be clear to one skilled in the art that the above embodiment maybe altered in many ways without departing from the scope of theinvention. Accordingly, the scope of the invention should be determinedby the following claims and their legal equivalents.

What is claimed is:
 1. A method for providing a desired curvature in airbearing surfaces of each of a plurality of sliders, comprising: a)performing the following steps in at least two installments: i)measuring a curvature of the air-bearing surface of each slider in a rowof sliders of the plurality; ii) determining a curvature differencebetween the curvature measured in step (i) and a final target curvaturefor each slider in the plurality; iii) while the sliders are still inthe row, scribing a pattern on a back surface of each slider in theplurality at each installment to correct for a portion of the curvaturedifference, wherein the pattern for each slider in the row has differentscribe lines; and iv) while the sliders are still in the row, scribing apartial length scribe line on the back surface of each slider in theplurality in a final installment to achieve the final target curvature,wherein the partial length scribe line does not extend entirely acrossthe back surface.
 2. The method of claim 1 wherein the scribe patternsare scribe lines located at scribe line locations spaced apart by adistance in the range of about 5-200 microns.
 3. The method of claim 2wherein the scribe lines are located at scribe line locations spacedapart by a distance in the range of about 20-80 microns.
 4. The methodof claim 3 wherein the scribe lines are located at scribe line locationsspaced apart by a distance in the range of about 35-55 microns.
 5. Themethod of claim 1 wherein the scribe patterns are crown scribe lines. 6.The method of claim 1 wherein the scribe patterns are camber scribelines.
 7. The method of claim 1 wherein the scribe patterns are scribelines located at scribe line locations spaced apart by a distancesufficient to ensure that neighboring scribe lines act independently. 8.The method of claim 1 further comprising the step of establishing a setof scribe line locations on the back surface.
 9. The method of claim 1wherein, in each installment, the average curvature change per scribeline is substantially equal to an average curvature contribution for allthe scribe line locations.
 10. The method of claim 1 wherein 1-3 linesare scribed in a final installment.
 11. The method of claim 1 wherein,in step iii, the portion of curvature difference for a first installmentor an intermediate installment is chosen such that the curvatureresulting from the scribe lines does not exceed the final targetcurvature.